Dr. Lisa M. Shulman, co-director of the University of Maryland Parkinson's Disease and Movement Disorders Center, made the surprise discovery recently that low-intensity workouts make the most difference in mobility and gait, which become a problem for most of those who sufferer from the disease. The information could lead to new advice from doctors and give hope to patients who can't manage a tough workout.

"Difficulty walking is the greatest cause of disability in people with Parkinson's disease," said Shulman, also a professor of neurology. "These results have important implications for how we manage Parkinson's disease, since low-intensity exercise can be done by most people with Parkinson's, and our patients frequently ask what type of exercise they should be doing."

Parkinson's is a degenerative neurological disorder that affects an estimated one in 100 people, usually seniors but not always, according to the Michael J. Fox Foundation, which helped sponsor Shulman's research. An estimated 1 million Americans are living with the disease.

For her study presented to the American Academy of Neurology this week, Shulman brought 67 Parkinson's patients ages 40 to 80 to the Baltimore VA Medical Center three times a week for three months. She randomly assigned them to one of three groups. The first walked for 50 minutes at their normal pace on a treadmill. Another did faster, shorter workouts on a treadmill. A third group did stretching and resistance exercises.

She documented how fast and far the patients could walk, and the low-intensity group made the most progress. She also found that overall Parkinson's symptoms such as tremors improved in those who did the stretching.

"At the end of the day, how well you can perform daily activities is what's really most important," she said, adding that she'll now recommend a combination of walking and stretching several times a week.

Thomas Manning, a retired Scaggsville home inspector and study participant, was so impressed by his results in the treadmill study that he bought a machine for his house after the study ended. He now walks daily for the physical benefits and for the boost in confidence he gets every time he finishes.

Manning, 78, said he can't stand using a cane and wants to stay as mobile as possible for as long as possible. That means he's less of a burden on his family and can continue his part-time job in the stockroom at a Napa auto parts store — which he says also provides more physical and mental exercise.

"Exercise is the name of the game," he said. "I'm a convert."

Other researchers have studied exercise for Parkinson's patients and seen benefits, though they aren't entirely sure how it works. They say that, in general, Parkinson's disease isn't completely understood. It's frequently misdiagnosed because there is not a test to confirm its presence.

Doctors believe Parkinson's results from the loss of cells in the brain that produce dopamine, a chemical that delivers signals within the brain that coordinate movement. As patients lose dopamine, they lose control.

The disease, thought to be caused by genetic and environmental factors, can progress at different rates in people, and symptoms can vary. Manning, for example, said his Parkinson's developed about a decade ago after he was bitten by a tick and came down with Lyme disease. His physical symptoms are not readily noticeable, except for a slight tremor sometimes in his right hand.

Tremors are a telltale sign of the disease. The Fox foundation says other symptoms are slowness of movement, balance problems, rigidity and reduced facial expression. They can also include cognitive impairment, mood disorders, sleeplessness, loss of ability to smell, drooling and low blood pressure.

The Fox foundation and other Parkinson's groups already advise sufferers to exercise, though some, like the National Parkinson Foundation, point to research supporting more intense exercise. Todd Sherer, Fox's chief program officer, said it's probably too early to recommend only low-intensity exercise and stretching, but based on the new research and other studies, doctors should be talking about exercise with all their Parkinson's patients.

Sherer said the foundation will continue to fund exercise research and hopes in coming years to make specific recommendations to the public and to doctors.

"This was a small study, but there was some real evidence in a controlled environment that exercise can be beneficial," he said. "Other studies have shown that exercise can be beneficial. What's important for the patient is to find exercise that they enjoy and is comfortable, because they have to keep doing it."

Dr. John Nutt, a professor of neurology at the Oregon Health & Science University, said he recommends exercise to his patients, emphasizing four components: strengthening, cardiovascular fitness, stretching and agility. He said Shulman's research offers "more evidence that I've been doing the right thing" in prescribing exercise in general.

But Nutt said that while Shulman's findings are "incredibly important," he wasn't ready to change his specific advice yet.

"What this [new research] is going to do is make a lot more practitioners interested in prescribing exercise," he said. "What brings maximum benefit, I don't know. I tend to think more is needed than simply walking at slow pace on the treadmill, but maybe in combination [with] the strength training."

He agreed that more research is needed on the impact of exercise on performance. It's also needed to assess the impact on the human brain to see if the course of the disease can be slowed. Past research conducted on rodents does support the theory that exercise benefits the mind. At the University of Southern California, researchers looked at rats and found that dopamine didn't increase in Parkinson sufferers with exercise, but it made its use more efficient — the brain was learning to compensate.

Shulman said she, too, would like to do more study. She's starting to look for research subjects to participate in a study of the impact of exercise on cognitive function in Parkinson's patients. She's interested in how the repetition involved in exercising improves human brain function.

That's what Beth Fisher also would like to show. Fisher is an associate professor of clinical physical therapy at the University of Southern California who was involved in rodent studies that showed high-intensity exercise improved brain function.

But she doesn't believe the findings contradict Shulman's. She defines high intensity as the ability to repeat steps and not necessarily the ability to improve aerobic capacity.

"We think the key ingredient is repetition and practice," she said. "Perhaps Dr. Shulman's patients did better because on the long, slower walks they practiced stepping way more."

She said she's not discounting aerobic training's effects on the brain, particularly in young patients with few symptoms, and will continue to study that in humans.

For now, she said. Shulman's findings reassure her that "there is nothing exercise isn't good for. I say do whatever you enjoy."